Moisture is required in lithographic printing to produce proper ink separation on the printing plate. Sufficient, but not excessive, dampening at the printing plate allows ink transfer from ink rollers where desired, and prevents ink from adhering to those portions which are free of printing areas. The use of spray heads for this purpose has met with varying success. An example of a relatively successful spray dampening system is disclosed in U.S. Pat. No. 3,949,688, issued Apr. 13, 1976, wherein individual positive displacement metering pumps are employed for supplying moisture to respective nozzles in a bank of adjacent nozzles for directing moisture toward the printing plate. This system has been found to accurately vary the moisture output of each nozzle while variation of a master drive controls overall bank output.
Although much sophistication has been achieved in supplying dampening liquid to spray nozzles, problems have remained in the basic function of the nozzle itself. Gum arabic and glycerin are common additives to water in lithographic dampening. Both materials have a tendency to dry or otherwise produce sticky deposits adjacent the discharge orifice of conventional nozzles, causing clogging and/or a distortion of the spray pattern and/or particle size desired for the printing process. Also, such additive deposits on the nozzle exterior secure lint, dust, and other foreign material common to a printing environment, causing further spray distortion.
The present invention overcomes the above difficulties in a lithographic spray dampening nozzle through the use of a modified structure which provides internal mixing of the dampening liquid with turbulent, expanding air and subsequent high velocity exit of the mixture through a single orifice having an abrupt, angular flare toward the outside.
The principal objects of the present invention are: to provide an improved self-cleaning nozzle for spraying dampening liquid in lithographic printing systems; to provide such a nozzle which effects mixing of a stream of dampening liquid with turbulent, expanding air within the nozzle; to provide such a nozzle including a wall positioned for substantially perpendicular impingement by high velocity air to effect high turbulence therein; to provide such a nozzle including an exit orifice forming surface which forms an acute angle and an obtuse angle respectively with the inner and outer surfaces of the wall in which the orifice is formed; to provide such a nozzle wherein the exit orifice may be elongated to shape the spray pattern; to provide such a nozzle which is compatible with many existing lithographic dampening systems; to provide such a nozzle which may be conveniently formed of molded synthetic resins; and to provide such a nozzle which is economical to manufacture, reliable and durable in operation, and which is particularly well adapted for its intended purpose.
Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.
The drawings constitute a part of the specification, include an exemplary embodiment of the present invention, and illustrate various objects and features of the self-cleaning nozzle.